The present invention relates to a non-scanning three-axis laser air data sensing system, including heterodyne operation for obtaining complete velocity information (i.e. direction and relative speed) with reference to particles or surfaces reflecting the provided laser beams.
At the present time, light detection and ranging (LIDAR) techniques for determining relative velocities between a laser source and airborne particulates that reflect light from the laser are known. To obtain information for more than one axis of velocity, these systems require either a scanning device for scanning the laser beam source to positions for sensing in different axes, or multiple sources and telescopes to provide the multiple axes. Scanners will increase the complexity of the circuitry used as well as the complexity of the packaging. Also, there are reliability issues for the moving parts involved. For multiple lasers and telescopes, the cost is increased drastically over a single telescope/laser system.
The technique to measure velocity involves Doppler principles where a frequency shift in the reflected signal is used for determining the relative fluid velocity. U.S. Pat. No. 5,164,784 illustrates schematically a device that uses a continuous wave Doppler Lidar with an enhanced signal to noise ratio, but this operates only in a single axis. The readout circuitry disclosed in U.S. Pat. No. 5,164,784, for analyzing the return signal of reflected light from a particle in order to determine the relative velocity of the particle, can be used with return signals obtained with the present invention to providing the output information. The present invention utilizes three separate laser sources to provide three axis information while eliminating the need for scanning. "Non-scanning", as used herein, means the laser beams have a pre-defined and non-moving path.